first = float(input("请输入第一个数："))
second = float(input("请输入第二个数："))
operator = input("请选择运算符：+-*/:")
if operator=='+':
    print(first+second)
elif operator=='-':
    print(first-second)
elif operator=='*':
    print(first*second)
elif operator=='/':
    if second==0:
        print("除数不能为0")
    else:
        print(first/second)